Magnetic Field Sensor Based on a Tri-Microfiber Coupler Ring in Magnetic Fluid and a Fiber Bragg Grating

Abstract

In this paper we propose and investigate a novel magnetic field sensor based on a Tri-microfiber coupler combined with magnetic fluid and a fiber Bragg grating (FBG) in a ring. A sensitivity of 1306 pm/mT was experimentally demonstrated in the range of magnetic fields from 0 to 15 mT. The reflection peak in the output spectrum associated with the FBG serves as a reference point allowing to avoid ambiguity in determining the spectral shift induced by the magnetic field. Due to its high sensitivity at low magnetic fields, the proposed structure could be of high interest in low field biosensing applications that involve a magnetic field, such as magnetic manipulation or separation of biomolecules.

Enhancing the Visibility of Vernier Effect in a Tri-Microfiber Coupler Fiber Loop Interferometer for Ultrasensitive Refractive Index and Temperature Sensing

“…Figure 1 shows a schematic diagram of the sensor. Since the structure is similar to that previously reported by us in [23] it will not be expanded upon further here. The waist section of tri-MFC was straight and suspended above the glass surface using two spacers fixed at both ends of a glass slide.…”

“…The low frequency envelope curve, which we will henceforth refer to as the Vernier spectrum, is due to ' beating' of the different interferences, from the Tri-MFC and PMF loop, for the two polarizations, respectively. From the above analysis we can conclude that in our previous work [23] the Vernier effect was not observed because the combination of the various physical parameters of the sensing system results in a total phase difference accumulated within the PMF loop and the MFC which is close to Nπ, where N is an integer. The significant distinction in this current work, is that the combination of the system parameters is deliberately chosen to provide a small total phase difference ( < ∆ < 2 + ), so in turn the visibility of the Vernier effect is enhanced.…”

“…Based on the analytical expression derived in our previous work [23], under particular RI and temperature conditions, the expanded transmission throughput from port 1 to port 2 via the Tri-MFC-PMF loop can be described by substituting the coupling ratio equation into the classic PMF loop equation as:…”

“…In this work, the structure is similar to our previous Tri-MFC-PMF loop structure [23] but the main novelty of this work is determining the condition of total phase delay accumulated over the PMF loop and Tri-MFC loop, to achieve a "strong" Vernier effect and furthermore providing an experimental demonstration that a high RI sensitivity with "clear" Vernier effect for the sensor can be achieved by optimizing the total phase delay of the Tri-MFC-PMF sensor. It has been established that the "strength" of Vernier effect can be directly related to and regulated by the total accumulated phase difference in the structure.…”

“…Chen et al demonstrated a highly sensitive micro-force sensor based on an MFC with sensitivity of ~3754 nm/N. In our previous work [23], we reported a Tri-MFC based Sagnac loop for sensing of magnetic field, where changes of the RI of the magnetic fluid surrounding the MFC were used to determine the magnetic field intensity.…”